1. Field of the Invention
The present invention relates to a transformer and a plasma generator.
2. Description of the Related Art
Atmospheric-pressure plasmas are used as a way of surface treatment in various applications, such as modification of and contamination removal from surfaces. In the case of applying, for example, bonding, printing, or coating to a resin material, preprocessing the material using an atmospheric-pressure plasma can improve wettability of a surface to be subjected to the application. This improvement allows the bonding, printing, or coating process to be favorably applied.
Generating the atmospheric-pressure plasma requires a high voltage, so that an inverter device needs to efficiently apply the high voltage and supply generated radical species to a load in a stable manner. In general, a plasma generator uses a high-voltage inverter device that provides an alternating-current output with an output voltage of ten-odd kilovolts or higher and an output power of several tens of watts or higher. A transformer used in such a high-voltage inverter device often employs an approach, such as increasing the number of turns of winding or dividing an output side winding, so as to obtain a sufficient magnetic flux density. Japanese Patent Application Laid-open No. 2012-135112 discloses a transformer that has divided output windings, and is provided with insulation layers of a flame-retardant tape between layers of the respective divided windings.
Providing insulating materials between the respective layers of the divided windings of the transformer increases the area occupied by the insulation layers between the windings by an amount corresponding to the division into the windings, leading to an increase in distributed capacitance. The high output voltage requires the number of turns be large, and, in addition, the distributed capacitance increases, so that the self-resonant frequency of the transformer decreases, and, from the viewpoint of the output, the frequency bandwidth of the output inductance of the transformer decreases. This causes the problem that the control range of the switching frequency decreases.
In view of the above, there is a need to provide a transformer that is capable of having a higher self-resonant frequency.